Excited State Decay Pathways Of Epigenetic DNA Nucleosides Tracked With Sub-20-fs UV Pulses

Modified nucleosides establish a second layer of information in DNA. Next to the four canonical bases, the DNA of higher organisms contains a total of four epigenetic deoxycytidine bases: m 5 dC, hm 5 dC, f 5 dC, and ca 5 dC. The regulation of the gene silencing and activation process can be linked to increased chemical diversity of these bases [1] . Here we characterized all four epigenetic nucleosides via the combination of sub-30-fs transient absorption (TA) spectroscopy [2] and molecular electronic structure calculations [3] .